FAQs

1. Acetic acid medium It is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. 316 stainless steel containing molybdenum is also suitable for high temperature and dilute acetic acid vapor. . For harsh requirements such as high temperature and high concentration of acetic acid or containing other corrosive media, high-alloy stainless steel or fluoroplastic valves can be selected. 2. Ammonia (Ammonia Hydroxide) Most metals and non-metals have slight corrosion in liquid ammonia and ammonia (ammonium hydroxide), and only copper and copper alloys are not suitable for use. 3. Salt water (sea water) The corrosion rate of ordinary steel in sodium chloride solution, sea water and salt water is not very high, and coating protection is generally required. Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions, usually 316 stainless steel is better. 4. Alkali (sodium hydroxide) Steel is widely used in sodium hydroxide solution below 80°C and 30% concentration. There are also many petrochemical plants that still use ordinary steel when the temperature is below 100°C and 75%. Although corrosion increases, it is economical. 5. Alcohols, ketones, esters, ethers Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc., ketone media include acetone, butanone, etc., ester media include various methyl and ethyl esters, and ether media include methyl ether, ethyl ether, etc. Butyl ether, etc., they are basically non-corrosive, and common materials can be applied. When selecting, a reasonable choice should be made according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers. Avoid mistakes when choosing sealing materials.

Advantages: 1. The fluid resistance is small. 2. Simple structure, relatively small size, light weight and easy maintenance 3. Good sealing performance. 4. It is not restricted by the installation direction, and the flow direction of the medium can be arbitrary. 5. No vibration and low noise. Disadvantage: Ball valves can be divided into floating ball valves, fixed ball valves, elastic ball valves and oil-sealed ball valves according to their structure. According to the channel, it can be divided into direct energy type, angle type and three-way type. The three-way type can be divided into T-shaped and L-shaped. According to the connection method, it can be divided into three types: threaded connection, flange connection and welding type. The following matters should be paid attention to when installing and maintaining the ball valve:. 1. Leave a position for the valve handle to rotate. . 2. Cannot be used for throttling. 3. The ball valve with drive mechanism should be installed upright.

1. The fault occurs at each connection. Cryogenic valves belong to this type of failure, such as valve packing running and freezing, valve seat and pipeline connecting flange leakage, valve screw sleeve at both ends of the tin filling thread leakage and so on. The valve stem packing is generally in the packing groove where the valve stem is close to the wall of the cold box. When the packing is uneven or not tight, or the valve stem is not straight or round, cryogenic liquid or gas will leak out along the gap in the packing. Due to the external cold transfer, the moisture in the air will freeze on the packing, freezing the valve stem. In this case, only use steam or hot water to heat the filler to open and close the valve. However, after the valve is opened and closed, the water accumulated in the packing will freeze again. Because the valve switch is laborious, the fire valve often causes the valve stem to twist and the hand wheel to break. Therefore, after the valve is overhauled, the packing should be evenly packed and tightened, and the compression nut should be tightened. During the overall leak test of the air separation plant, the leakage at the lower valve stem packing should also be checked, and this problem should be solved before the cold start. The common causes of flange leakage are unsmooth and uneven sealing surface, insufficient pipeline compensation, uneven bolt tightening, improper bolt material, etc. Both ends of the outer threaded sleeve of the valve stem are connected with tin-filled threads, which are prone to cracks and leakage after long-term use. When pressure test leaks, if such a leak is found, It is best to pull out the valve stem and refill it with tin and tighten it, and it is best to use silver welding. Cryogenic valve is an equipment that should be maintained frequently during the normal operation of air separation equipment. We should have high standards, strict requirements, careful maintenance and good use. 2. The fault occurred on the top of the valve. The valve top (valve head) of this kind of valve is movably connected with the valve stem, so that the two sealing surfaces can be "automatically aligned" when the valve is closed. After long-term use, titanium, nickel, zirconium, Monel and alloy valves are sometimes damaged by the anti-return gasket, which causes the locking nut to loosen, and finally the valve top falls off when the valve is opened. At this time, the valve will lose its closing function. Sometimes the damage of the lock nut is caused by improper material, replaced by cold brittle metal. Another common fault is that the valve top is not tightly closed, that is, the valve is leaking. The common reason is that the valve top and the sealing surface of the valve seat are crushed by hard objects (such as silica gel, metal shavings, welding slag and other hard objects), forming dents. In this case, the marine valve often uses a lot of effort to close the valve, and the result is that the pressure injury is aggravated. Sometimes the valve stem center line is not perpendicular to the valve seat sealing surface (valve surface), or the valve top and valve surface are worn out due to long-term use, which will cause the valve to leak. 3. The failure occurred on the valve stem. The more common fault is the wear of the thread on the valve stem and screw sleeve, and the ceramic valve [door makes the valve unable to close. Generally, the threaded thread of the valve stem is not easy to wear out, and the female thread on the screw sleeve (brass) is easy to be damaged. The reason is mostly because the valve is opened with too much force, or it is still twisted hard after it is opened or closed, causing the thread to bite. Sometimes the thread is completely "bitten" and the valve can only be opened but not closed. To close the valve, you can only use a temporary bolt to push the valve stem inward and wait for maintenance before repairing. To prevent this kind of failure, the most important thing is not to use too much force when opening and closing the valve, and do not open or close hard when opening or closing the valve.